1. Field of the Invention
The present invention generally relates to the art of processing particulate solids and specifically to a device or pump for conveying and/or compressing such solids.
2. Description of the Prior Art
My above-mentioned copending U.S. patent application discloses a method of pumping a particulate solid material and a pump (also referred to as a rotary channel pump or RCP) for compressing such particulate materials.
That pump utilizes a mechanism known as "drag-flow" and is discussed in detail in my above-mentioned U.S. Pat. No. 5,223,199 the disclosure of which is incorporated herein by way of reference.
Drag flow devices for processing of solids have been disclosed in U.S. Pat. Nos. 4,516,674 and 5,051,041 to Firth, in U.S. Pat. No. 4,421,412 to Hold and Tadmore as well as in U.S. Pat. No. 4,231,709 to Valsamis. Further art pertaining to technological background as cited in my copending European patent application 91810547, corresponding to published European Patent Application No. 467,842 and U.S. Pat. No. 5,223,199, is identified as follows: EP-A-0 326 036, US-A-3 884885 US-A-4 102 109 and US-A-4 142 805.
Generally, processing of particulate solids, (i.e. in the form of particles) which have an "apparent" or "bulk" density that is significantly lower than the structural density of the material per se, such as "plastics" scrap, may present processing problems when conveying and/or feeding the material into a processor, e.g. when recycling thermoplastic scrap, waste, or refuse having a low bulk density into an extruder. In fact, future economics of using and notably of recycling plastics will depend substantially upon the way in which low bulk density solids can be processed economically.
As set forth in my above-mentioned U.S. patent the rotary channel pump disclosed therein is eminently suitable for compaction or pumping of particulate solids regardless of their bulk weight. In a preferred embodiment of the pump of my U.S. patent the particulate solids are precompacted before they are fed into the rotary channel pump, e.g. by a reciprocating ram.
It has been found that precompaction of the particulate solids according to the said embodiment of the rotary channel pump disclosed in my U.S. patent application can be achieved advantageously by means of a rotary feeder of the type operating essentially by displacement flow.